This invention relates to an amine recovery method and apparatus, and a decarbonation apparatus having the amine recovery apparatus.
In recent years, thermal power equipment and boiler equipment have used large amounts of coal, heavy oil or superheavy oil as fuels. From the points of view of air pollution control and Earth environment purification, there have been problems in how to decrease the quantities and concentrations of emissions of sulfur oxides (mainly sulfur dioxide), nitrogen oxides, and carbon dioxide. Suppression of carbon dioxide emission, in particular, has recently been investigated, together with emission control of flon gas and methane gas, from the viewpoint of global warming. For this purpose, methods for removing carbon dioxide, such as PSA (pressure swing) method, membrane separation, and absorption by reaction with basic compounds, are under study.
As an example of a method for removing carbon dioxide with the use of basic compounds, Japanese Unexamined Patent Publication No. 1993-184866 (related U.S. Pat. No. 5,318,758) proposes a method which performs decarbonation by using an aqueous solution of an amine compound (hereinafter referred to simply as an amine) as a solution for absorbing carbon dioxide. In this method, the reaction between carbon dioxide and the amine compound is an exothermic reaction. Thus, the temperature of the absorbing solution in a carbon dioxide absorption section rises to raise the vapor pressure of the amine. That is, the amine-containing absorbing solution evaporates owing to the temperature increase. As a result, the amount of the amine compound accompanying a decarbonated gas increases. Thus, a water washing section is provided in an absorption tower, and the decarbonated gas and washing water are subjected to vapor-liquid contact in the water washing section, whereby the amine compound accompanying the decarbonated gas is recovered into a liquid phase.
Concretely, the above-mentioned Japanese Unexamined Patent Publication No. 1993-184866 discloses a decarbonation apparatus as shown in FIGS. 2 and 3.
In FIG. 2, the reference numeral 1 denotes an absorption tower, 2 a carbon dioxide absorption section, 3 a water washing section, 4 an exhaust gas supply section, 6 is an absorbing solution supply port, 7 a nozzle, 8 a liquid reservoir in the water washing section, 9 a circulating pump, 10 a cooler, 11 a nozzle, 12 an absorbing solution discharge port, 13 a blower, 14 an exhaust gas supply port, 15 an exhaust gas cooler, 16 a circulating pump, 17 a cooler, 18 a nozzle, and 19 a drainage line.
Although a detailed explanation is omitted, a combustion exhaust gas supplied through the exhaust gas supply port 14 is cooled by the cooling tower 15, and then fed to the absorption tower 1. In the carbon dioxide absorption section 2 of the absorption tower 1, the fed combustion exhaust gas is brought into countercurrent contact with an absorbing solution supplied through the absorbing solution supply port via the nozzle 7. As a result, carbon dioxide in the combustion exhaust gas is absorbed and removed by the absorbing solution. The loaded absorbing solution, which has absorbed carbon dioxide, is sent to a regeneration tower (not shown) through the absorbing solution discharge port 12. In the regeneration tower, the loaded absorbing solution is regenerated, and fed again from the absorbing solution supply port 6 to the absorption tower 1.
On the other hand, the combustion exhaust gas decarbonated in the carbon dioxide absorption section (i.e., decarbonated exhaust gas) ascends, accompanied by a large amount of an amine vapor, due to a temperature rise ascribed to an exothermic reaction between carbon dioxide and an amine compound in the carbon dioxide absorption section 2. The ascending decarbonated exhaust gas passes through the liquid reservoir 8, and heads toward the water washing section 3. In the water washing section 3, reserved water in the liquid reservoir 8 is transported by the circulating pump 9, cooled by the cooler 10, and then supplied to the water washing section 3 as washing water through the nozzle 11. As a result, this washing water and the decarbonated exhaust gas make countercurrent contact in the water washing section 3, whereby the amine compound in the decarbonated exhaust gas is recovered into the liquid phase.
FIG. 3 is characterized by improving the amine recovering ability by utilization of regeneration tower refluxed water. In FIG. 3, the reference numeral 21 denotes an absorption tower, 22 a carbon dioxide absorption section, 23 a water washing section, 24 an exhaust gas supply port, 25 an exhaust gas discharge port, 26 an absorbing solution supply port, 27 a nozzle, 28 a regeneration tower ref luxed withdrawn water supply port, 29 a nozzle, 30 a cooler, 31 a nozzle, 32 a charging section, 33 a circulating pump, 34 a make-up water supply line, 35 an absorbing solution discharge pump, 36 a heat exchanger, 37 a cooler, 38 a regeneration tower, 39 a nozzle, 40 a lower charging section, 41 a reboiler, 42 an upper charging section, 43 a refluxed water pump, 44 a carbon dioxide separator, 45 a carbon dioxide discharge line, 46 a cooler, 47 a nozzle, 48 a refluxed water supply line, and 49 a combustion gas supply blower.
Although a detailed explanation is omitted, a combustion exhaust gas supplied by the combustion gas supply blower 49 is cooled by the cooling tower 30, and then fed to the absorption tower 21. In the carbon dioxide absorption section 22 of the absorption tower 21, the fed combustion exhaust gas is brought into countercurrent contact with an absorbing solution supplied through the absorbing solution supply port 26 via the nozzle 27. As a result, carbon dioxide in the combustion exhaust gas is absorbed and removed by the absorbing solution. The loaded absorbing solution, which has absorbed carbon dioxide, is sent to the regeneration tower 38 by the absorbing solution discharge pump 35 through the absorbing solution discharge port 12. In the regeneration tower 38, the loaded absorbing solution is regenerated, and fed again to the absorption tower 21 through the absorbing solution supply port 26.
On the other hand, the combustion exhaust gas decarbonated in the carbon dioxide absorption section 22 (i.e., decarbonated exhaust gas) ascends, accompanied by a large amount of an amine vapor, owing to a temperature rise ascribed to an exothermic reaction between carbon dioxide and an amine compound in the carbon dioxide absorption section 22. The ascending decarbonated exhaust gas heads toward the water washing section 23. In the water washing section 23, part of regeneration tower refluxed water withdrawn as washing water is supplied to the water washing section 23 through the regeneration tower ref luxed withdrawn water supply port 28 via the nozzle 29. As a result, this washing water and the decarbonated exhaust gas make countercurrent contact in the water washing section 23, whereby the amine compound in the decarbonated exhaust gas is recovered into the liquid phase.
However, according to the above-described conventional decarbonation apparatus shown in FIG. 2, in particular, the water washing section is provided as one stage. Thus, the concentration of amine recovered by the washing water is so high that the recovery of amine is insufficient. As a result, amine accompanies the decarbonated exhaust gas, and is released to the outside of the decarbonation process system. Consequently, amine is wasted, causing a concern about an increase in the operating cost, etc.
The present invention has been accomplished in the light of the foregoing problems. Its object is to provide an amine recovery method and apparatus, and a decarbonation apparatus equipped with the amine recovery apparatus, the amine recovery method and apparatus being capable of efficiently recovering an amine compound accompanying a decarbonated exhaust gas in a decarbonation process in which carbon dioxide is removed from a gas containing carbon dioxide with the use of an amine compound-containing absorbing solution.
An amine recovery method as a first invention for solving the above problems is an amine recovery method for recovering an amine compound accompanying a decarbonated exhaust gas by bringing the decarbonated exhaust gas into vapor-liquid contact with washing water in a water washing section, the decarbonated exhaust gas having had carbon dioxide absorbed and removed by vapor-liquid contact with an absorbing solution containing the amine compound in a carbon dioxide absorption section, characterized in that
the water washing section is constituted in a plurality of stages, and
recovery of the amine compound accompanying the decarbonated exhaust gas is performed sequentially in the water washing sections in the plural stages.
Thus, according to the amine recovery method as the first invention, the water washing section is constituted in a plurality of stages, and recovery of the amine compound accompanying the decarbonated exhaust gas is performed sequentially in the water washing sections in the plural stages. Consequently, the amine compound accompanying the decarbonated exhaust gas can be recovered very efficiently, and the operating cost can be reduced.
An amine recovery method as a second invention is the amine recovery method of the first invention, characterized in that
regeneration tower refluxed water is supplied as washing water to the water washing section.
Thus, according to the amine recovery method of the second invention, the concentration of amine contained in washing water of the water washing section is decreased, and the amine recovery ability is further enhanced.
An amine recovery method as a third invention is the amine recovery method of the first or second invention, characterized in that
washing water is withdrawn from the water washing section in the succeeding stage and supplied to the water washing section in the preceding stage.
Thus, according to the amine recovery method of the third invention, the concentration of amine contained in washing water of the water washing section in the preceding stage is decreased to enhance the amine recovery ability in the water washing section in the preceding stage. In accordance with this advantage, the concentration of amine contained in washing water of the water washing section in the succeeding stage is also further decreased to further enhance the amine recovery ability as a whole.
An amine recovery method as a fourth invention is the amine recovery method of the first, second or third invention, characterized in that
demisters are provided at outlets of the carbon dioxide absorption section and the water washing sections in the respective stages, and
an absorbing solution mist and a washing water mist accompanying the decarbonated exhaust gas are removed by the demisters.
Thus, according to the amine recovery method of the fourth invention, it can be prevented that part of the absorbing solution mist fed to the carbon dioxide absorption section and part of the washing water mist fed to the water washing sections in the respective stages are released to the outside of the system together with the decarbonated exhaust gas, causing losses in water and amine compound.
An amine recovery apparatus as a fifth invention is an amine recovery apparatus for recovering an amine compound accompanying a decarbonated exhaust gas by bringing the decarbonated exhaust gas into vapor-liquid contact with washing water in a water washing section, the decarbonated exhaust gas having had carbon dioxide absorbed and removed by vapor-liquid contact with an absorbing solution containing the amine compound in a carbon dioxide absorption section, characterized in that
the water washing section is constituted in a plurality of stages, and
recovery of the amine compound accompanying the decarbonated exhaust gas is performed sequentially in the water washing sections in the plural stages.
Thus, according to the amine recovery apparatus of the fifth invention, the water washing section is constituted in a plurality of stages, and recovery of the amine compound accompanying the decarbonated exhaust gas is performed sequentially in the water washing sections in the plural stages. Consequently, the amine compound accompanying the decarbonated exhaust gas can be recovered very efficiently, and the operating cost can be reduced.
An amine recovery apparatus as a sixth invention is the amine recovery apparatus of the fifth invention, characterized in that
regeneration tower refluxed water is supplied as washing water to the water washing section.
Thus, according to the amine recovery apparatus of the sixth invention, the concentration of amine contained in washing water of the water washing section is decreased, and the amine recovery ability is further enhanced.
An amine recovery apparatus as a seventh invention is the amine recovery apparatus of the fifth or sixth invention, characterized in that
washing water is withdrawn from the water washing section in the succeeding stage and supplied to the water washing section in the preceding stage.
Thus, according to the amine recovery apparatus of the seventh invention, the concentration of amine contained in washing water of the water washing section in the preceding stage is decreased to enhance the amine recovery ability in the water washing section in the preceding stage. In accordance with this advantage, the concentration of amine contained in washing water of the water washing section in the succeeding stage is also further decreased to further enhance the amine recovery ability as a whole.
An amine recovery apparatus as an eighth invention is the amine recovery apparatus of the fifth, sixth or seventh invention, characterized in that
demisters are provided at outlets of the carbon dioxide absorption section and the water washing sections in the respective stages, and
an absorbing solution mist and a washing water mist accompanying the decarbonated exhaust gas are removed by the demisters.
Thus, according to the amine recovery apparatus of the eighth invention, it can be prevented that part of the absorbing solution mist fed to the carbon dioxide absorption section and part of the washing water mist fed to the water washing sections in the respective stages are released to the outside of the system together with the decarbonated exhaust gas, causing losses in water and amine compound.
A decarbonation apparatus as a ninth invention is characterized by having the amine recovery apparatus of the fifth, sixth, seventh or eighth invention in an absorption tower.
Thus, the decarbonation apparatus of the ninth invention has the amine recovery apparatus of the fifteenth, sixth, seventh or eighth invention in an absorption tower. Hence, the decarbonation apparatus is an apparatus with a high ability to recover the amine compound and involving a low operating cost.